The present invention pertains to the field of catheter systems, and more particularly, to therapeutic catheters for the electrophysiological treatment of cardiac rhythm disturbances.
Normal sinus rhythm of the heart begins with the sinoatrial node (or xe2x80x9cSA nodexe2x80x9d) generating a depolarization wave front, or electrical impulse. This impulse causes adjacent myocardial tissue cells in the right and left atria to depolarize. The electrical impulse uniformly propagates across the right and left atria and the atrial septum to the atrioventricular node (or xe2x80x9cAV nodexe2x80x9d), causing the atria to contract and empty blood from the atria into the ventricles. The electrical impulse propagates through the AV node to the atrioventricular bundle (or xe2x80x9cHIS bundlexe2x80x9d), where it further propagates across the ventricles, causing the ventricles to contract. The AV node regulates the propagation delay to the HIS bundle, so that atrial systole occurs during ventricular diastole. This coordination of the electrical activity results in the described, organized sequence of myocardial contraction leading to a normal heartbeat.
Sometimes aberrant conductive pathways develop in heart tissue, which disrupt the normal path of depolarization events. For example, anatomical obstacles, called xe2x80x9cconduction blocks,xe2x80x9d can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called xe2x80x9creentry circuits,xe2x80x9d disrupt the normal activation of the atria or ventricles. As a further example, localized regions of ischemic myocardial tissue may propagate depolarization events slower than normal myocardial tissue. The ischemic region, also called a xe2x80x9cslow conduction zone,xe2x80x9d creates the substrate for errant, circular propagation patterns, called xe2x80x9ccircus motion.xe2x80x9d The circus motion also disrupts the normal depolarization patterns, thereby disrupting the normal contraction of the heart tissue.
The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms, called arrhythmias. An arrhythmia can take place in the atria, for example, as in atrial tachycardia (AT) or atrial flutter (AF). The arrhythmia can also take place in the ventricle, for example, as in ventricular tachycardia (VT). In treating arrhythmias, it is sometimes essential that the location of the sources of the aberrant pathways (called focal arrhythmia substrates) be located. Once located, the focal arrhythmia substrate can be destroyed, or ablated, e.g., by surgical cutting, or the application of heat. In particular, ablation can remove the aberrant conductive pathway, thereby restoring normal myocardial contraction. An example of such an ablation procedure is described in U.S. Pat. No. 5,471,982, issued to Edwards et al.
Alternatively, arrhythmias may be treated by actively interrupting all of the potential pathways for atrial reentry circuits by creating complex lesion patterns on the myocardial tissue. An example of such a procedure is described in U.S. Pat. No. 5,575,810, issued to Swanson et al.
Frequently, a focal arrhythmia substrate resides at the base, or within, one or more pulmonary veins, wherein the atrial tissue extends. The automaticity created by these substrates results in ectopic atrial tachycardia. Although the effect caused by the depolarization wavefront propagating from the pulmonary vein containing the substrate resembles that caused by re-entrant pathways within the atria, the atrial fibrillation is actually caused by a single focal arrhythmia substrate within the pulmonary vein. Arrhythmia substrates residing at the base of, or within, a pulmonary vein may alternatively participate in circuit with the depolarization wavefront propagating around a single vein or within a slow conduction zone residing near or within the vein.
Current techniques of eradicating these substrates include steering a conventional ablation catheter within the target pulmonary vein and mapping this region to pinpoint the substrate. However, this is a time consuming and difficult process. Either extensive mapping must be performed within the pulmonary vein to accurately locate the target ablation site, or multiple lesions must be created to, in effect, xe2x80x9ccarpet bombxe2x80x9d the substrate. Moreover, the substrate may be located deep within the pulmonary vein, thereby making the manipulations required to steer the catheter""s distal tip to the target site difficult.
Another technique involves creating circumferential lesions in endocardial and surrounding tissues, e.g., in and around pulmonary veins, in the inferior vena cava, the superior vena cava, and the sinus coronary, to thereby isolate focal arrhythmia substrates. A variety of catheters with electrodes mounted on their distal ends may be used in performing this technique, an especially popular type being balloon catheters. When balloon catheters are used, at least a portion of the surface area of the balloon typically comprises an electrode that performs the ablation.
There are drawbacks to using conventional balloon catheters for creating circumferential lesions in endocardial and surrounding tissues. A serious drawback is that due to their typically large profiles, known balloon catheters tend to completely block blood flow in the vein or artery where the balloon is inflated. Furthermore, these balloon catheters may not work with 150 watt/2.0 amp maximum radio frequency (RF) generators because of the increased surface area created by the inflated balloon. Yet another drawback is that different sized balloon catheters are required for the different sizes of veins and arteries.
Accordingly, there is a need for a balloon catheter that can electrically isolate veins by creating circumferential lesions in tissue, such as in endocardial and surrounding tissue, without substantially obstructing the flow of blood, and that can be used over a wide range of different sized veins and arteries. Furthermore, there is a need for a balloon catheter that can be used with 150 watt/2 amp generators.
The present invention addresses the aforementioned problems and is directed to methods and apparatus for creating circumferential lesions in and around veins, coronary vessels, and other parts of the body, without substantially obstructing blood flow. In particular, the present invention is designed to ablate tissue within a fluid carrying vessel, such as a blood vessel, while at the same time providing open channels for the fluid to flow around the apparatus.
In a first aspect of the present inventions, an ablation catheter is provided. The ablation catheter includes an elongate catheter body and an electrode structure mounted on a distal end of the catheter body, wherein the electrode structure includes a plurality of radially disposed inflatable chambers, e.g., four chamber.
In the preferred embodiment, each of the inflatable chambers has an exterior wall that peripherally surrounds an interior region. By way of non-limiting example, the exterior wall can be common to the plurality of inflatable chambers, in which case, adjacent inflatable chambers will be separated by a rib. Or each inflatable chamber comprises a distinct wall, in which case, the exterior wall will be formed by an aggregate of the plurality of distinct walls. The electrode structure is capable of delivering RF ablation energy. Alternatively, the electrode structure can be capable of delivering other types of ablative energy, such as microwave, ultrasonic, cryoablation, resistive heating, etc. In the preferred embodiment, ablation energy is delivered by the exterior wall of the electrode structure. By way of non-limiting example, the exterior wall can be formed of a microporous material or a conductive material.
In the preferred embodiment, the elongate catheter body is composed of an inner shaft having an inner shaft lumen, a stiffening mandrel disposed within the inner shaft lumen, and an outer shaft having an outer shaft lumen, wherein the inner shaft is disposed within the outer shaft lumen. The outer shaft includes a plurality of inflation lumens in communication with the interior regions of the inflatable chambers, which deliver an inflation medium to the inflatable chambers, and the inner shaft includes a plurality of lumens that house electrical leads for delivering ablation energy to the electrode structure. The ablation catheter may have a handle mounted on the proximal end of the catheter body and a radiopaque marker disposed on the distal end of the catheter body, thereby allowing the physician to properly orient the ablation catheter within the patient""s body.